This invention relates to the art of vacuum cleaning and, more particularly, to improvements in vacuum cleaners and filter bags for removing particulate materials from an airstream flowing therethrough.
The invention is particularly applicable to canister type vacuum cleaners of the character having a canister chamber wherein large particles in particle laden air carried into the chamber are extracted upstream from a filter through which the air flows and upon which finer particular material collects during a vacuum cleaning operation. At the same time, as will become apparent from the disclosure herein, the invention is applicable to canister and other vacuum cleaning apparatus such as upright vacuum cleaners in which particle laden air flows into a filter bag of air pervious material in which larger particles are collected and onto the inner surface of which smaller particulate material adheres as the cleaned air flows through the pervious bag material.
A canister type vacuum cleaner of the character to which the invention is particularly applicable is shown in U.S. Pat. No. 5,248,323 to Stevenson which is incorporated herein by reference for background information. Such a canister type vacuum cleaner includes a reduced velocity chamber with a high velocity air inlet through which particle laden air is drawn by a motor driven fan downstream of the air inlet and supported on top of the canister. A conical filter unit of air pervious material extends downwardly into the canister from the motor driven fan for removing and collecting dirt, debris and other particulate material carried by the airstream coming into the canister. Particle laden air is directed into the chamber so as to have a swirling or vortex flow configuration between the air inlet and filter unit so that large particles carried into the chamber with the inlet air are extracted by the vortex or cyclonic action of the air in the chamber. Thereafter, the air with minute particles still entrained therein is pulled upwardly through the conical filter unit which captures the minute particles, and the cleaned air is exhausted through an exhaust passage or passages above the canister.
Certain particles of dirt and other debris flowing into the canister, herein characterized as particles or particulate matter in an intermediate category, are not heavy enough to be extracted from the airstream by the swirling motion of the air and, consequently, impact and/or abrade against the inner wall of the canister and/or the filter element and break up into smaller particles which remain entrained in the airstream flowing through the filter and thus adhere to the later. It is of course the purpose of the filter to capture smaller particulate material so that the air exhausted from the vacuum cleaner is clean, but the breaking up of certain particles and debris in the intermediate category as described above results in the filter being more quickly clogged and, therefore, further results in requiring frequent cleaning or replacement of the filter in order to maintain a desired degree of efficiency in operation of the vacuum cleaner. Such filter clogging is also a problem with canister and/or upright type vacuum cleaners which employ a disposable filter bag through which particle laden air flows during a vacuum cleaning operation. In this respect, heavy particles will settle in the bottom of the bag, but certain debris in the intermediate category referred to above which is not heavy enough to be extracted from the airstream will remain entrained therein and will adhere to or break up and adhere to the inner surface of the bag so as to more quickly clog the bag than would be the case if these materials could be removed from the airstream before impinging against the inner surface of the filter bag. Often, when a canister type vacuum cleaner is opened for cleaning the filter unit, the canister chamber does not appear to be very full of debris and, similarly, when a canister or upright vacuum cleaner is opened to replace the filter bag therein, the filter bag does not appear to be very full, whereby it becomes obvious that the filter or filter bag has become clogged to the extent that cleaning or replacement is required long before the available capacity of the canister or filter bag is efficiently used. In either event, the frequent cleaning of the filter in a canister type vacuum cleaner is time consuming, and the frequent replacement of filter bags in canister or upright vacuum cleaners is both time consuming and expensive.